The present invention generally relates to heat exchangers and, more particularly, to integrated heat exchangers.
Fuel tank inerting systems (FTIS) typically use bleed air from engines that is fed into air separation modules (ASM) for the purpose of inerting fuel tanks. It is necessary to cool the bleed air to an acceptable temperature, for example about 200 deg F. The bleed air can be cooled with a heat exchanger that uses outside atmospheric air as a heat sink.
A prior art FTIS heat exchanger 20 is depicted in FIG. 1. The prior art FTIS heat exchanger 20 is positioned within a ram air plenum 21. The cooling can be induced by a fan (not shown) that is part of an environmental control system (ECS) air cycle machine. The prior art FTIS heat exchanger 20 comprises a separate entity and can be placed upstream of a prior art ECS heat exchanger 22 in series relative to a flow of ram air 23. For configurations that have an in-series placement, the flow of ram air 23 can pass through the upstream prior art FTIS heat exchanger 20 before entering the downstream prior art ECS heat exchanger 22. In such a configuration as used on aircraft applications, the inerting heat load from the prior art FTIS heat exchanger 20 can end up being dumped on the prior art ECS heat exchanger 22. The dumping of the inerting heat load onto the prior art ECS heat exchanger 22 has a negative impact on the performance of the ECS.
The prior art FTIS heat exchanger 20 also can negatively impact the fluid dynamics within the ram air plenum 21. A diagram of a computational fluid dynamic (CFD) analysis showing velocity vectors of the prior art configuration is shown in FIG. 2a. A diagram of a CFD analysis showing pressure of the prior art configuration is shown in FIG. 2b. FIGS. 2a and 2b depict CFD analyses along a center slice 24 (see FIG. 1) of FIG. 1. As can be seen, the prior art ECS heat exchanger 22 experiences an additional pressure drop in the area immediately downstream of the prior art FTIS heat exchanger 20. The additional pressure drop induced by the prior art FTIS heat exchanger 20 adds to the power consumed by the fan which comes at the expense of ECS performance on the ground. The net effect is an increase in the cabin stabilized temperature above the specified value for the cabin.
U.S. Patent Application No. 2005/0235659, describes an air conditioning system heat exchanger connected to a second heat exchanger by a closable line and valve. The second heat exchanger can be an on-board inert gas generating system (OBIGGS) or an on-board oxygen generating system (OBOGS) heat exchanger. The closable line allows the ram air that passes through the second heat exchanger to be used for the air conditioning system when the second system (OBIGGS or OBOGS) is not in use. Although the described system may provide additional cooling for the air conditioning system when the OBIGGS is not in use, the closable line and valve adds complexity to the system. Further, the disturbances in the ram flow (turbulence) caused by the OBIGGS heat exchanger can reduce the efficiency of the air conditioning heat exchanger.
As can be seen, there is a need for systems that can reduce the negative impact that the OBIGGS heat exchangers have on the ECS heat exchangers. Further, systems are needed wherein the flow disturbances associated with the OBIGGS heat exchangers are reduced. Moreover, systems are needed that reduce the negative impact of the pressure drop caused by the OBIGGS heat exchanger.